Your truck may be loosing its fuel prime. Connect a fuel pressure gauge. After truning off the engine the fuel system should hold pressure. If it does not chances are the fuel is draining back into the fuel tank due to a faulty pump assembly. If the fuel bleeds of slowly that may be ok as long the pressure comes back a soon a you turn to key on to start the engine.

...does not help. Fuel pressure is steady at 60psi at idle and under load. 3000 miles before the hard starting problem surfaced, a new fuel filter and spark plugs were installed (maintenance items). The fa...